A microphone, for example, a MEMS microphone, comprises a capacitive transducer that can be modelled as a variable capacitor having a variable capacitance being dependent on a sound pressure that impacts on a membrane of the variable capacitor. The transducer may comprise a diaphragm and a backplate. By an acoustical input, in particular a pressure wave, the diaphragm may be deflected such that the distance between the diaphragm and the backplate changes, resulting in a change of the capacitance of the transducer. When the transducer is subjected to very high sound pressure levels (SPL), the diaphragm may contact the backplate so that an acoustical collapse of the diaphragm may occur.
In order to operate the microphone, a bias voltage is usually applied to the transducer, in particular between the diaphragm and the backplate of the transducer. By adjusting the value of the bias voltage, the sensitivity of the transducer may be adjusted. To increase the dynamic range of the MEMS microphone, its bias voltage can be reduced before the sound pressure level gets so high that an acoustical collapse would take place.
The transducer is usually coupled to a preamplifier that generates an amplified output signal in dependence on the sound pressure that impacts on the membrane of the transducer. A reduction of the bias voltage in order to prevent an acoustical collapse can, however, cause the preamplifier DC input voltage to move away from its biasing operation point and potentially bring it to saturation, which will turn into a lack of sensitivity and/or distortion.